Alert archive / Pennsylvania / Flash Flood Warnings in 2026
Flash Flood Warning 124, NWS Philadelphia/Mount Holly
NWS Philadelphia/Mount Holly issued this flash flood warning at Aug 20, 2026, 6:26 PM EDT for Mercer County, New Jersey; Bucks County, Montgomery County, Philadelphia County, Pennsylvania. It was in force for 4 hr. 6 reports came from inside the area while it was in force.
The area
The outline as issued, with what was reported inside it.
The facts
- Issued
- Aug 20, 2026, 6:26 PM EDT (22:26 UTC)
- Expired
- Aug 20, 2026, 10:30 PM EDT
- In force
- 4 hr
- Issued by
- NWS Philadelphia/Mount Holly
- Area
- Storm-based polygon
- Flood severity
- None
Counties Mercer County, NJ, Bucks County, PA, Montgomery County, PA, Philadelphia County, PA
The radar
The Philadelphia radar (KDIX), 53 km from the middle of the area, began a volume at 22:25 UTC, the scan nearest the moment this went out.
Open the radar archive at this moment
The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.
What was reported inside it
| Time | Report | Where | Remark |
|---|---|---|---|
| Aug 20, 7:07 PM EDT | FLASH FLOOD | 1 E Willow Grove, PA | Storm dropped 2 inches of rain resulting in street flooding. |
| Aug 20, 7:30 PM EDT | FLASH FLOOD | Warminster, PA | Multiple water rescues in Warminster. Time estimated. |
| Aug 20, 9:00 PM EDT | RAIN 2 | 1 E Willow Grove, PA | Mesonet station EW1527 Willow Grove. |
| Aug 20, 9:00 PM EDT | RAIN 2.27 | 1 Nw Willow Grove, PA | Mesonet station FW1161 Willow Grove. |
| Aug 20, 9:02 PM EDT | RAIN 1.3 | Trenton Mercer Airport, NJ | ASOS station KTTN Trenton. |
| Aug 20, 9:07 PM EDT | RAIN 2.04 | 1 Ese Hatboro, PA | Mesonet station GW6756 HATBORO. |
Local storm reports filed while the alert was in force, from inside its polygon or its counties.
The nearest sounding before it
Brookhaven, NY (KOKX), launched 12:00Z, 10.4 hours before the alert went out and 181 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.
- Mixed-layer CAPE
- 0 J/kg
- Mixed-layer CIN
- No buoyant parcel
- Mixed-layer LCL
- 1229 m above ground
- 0-6 km bulk shear
- 37 kt
- 0-1 km storm-relative helicity
- -27 m²/s²
- 0-3 km storm-relative helicity
- 21 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
443
WGUS51 KPHI 202226
FFWPHI
NJC021-PAC017-091-101-210230-
/O.NEW.KPHI.FF.W.0124.260820T2226Z-260821T0230Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Mount Holly NJ
Issued by National Weather Service New York NY
626 PM EDT Thu Aug 20 2026
The National Weather Service in Mount Holly has issued a
* Flash Flood Warning for...
Mercer County in central New Jersey...
Southeastern Bucks County in southeastern Pennsylvania...
East Central Montgomery County in southeastern Pennsylvania...
Northeastern Philadelphia County in southeastern Pennsylvania...
* Until 1030 PM EDT.
* At 626 PM EDT, Doppler radar indicated thunderstorms producing
heavy rain across the warned area. Up to 0.5 inches of rain have
fallen. The expected rainfall rate is 1 to 2 inches in 1 hour.
Additional rainfall amounts of 1 to 2 inches are possible in the
warned area. Flash flooding is ongoing or expected to begin
shortly.
HAZARD...Flash flooding caused by thunderstorms.
SOURCE...Radar indicated.
IMPACT...Flash flooding of small creeks and streams, urban areas,
highways, streets and underpasses as well as other poor
drainage and low-lying areas.
* Some locations that will experience flash flooding include...
Philadelphia, Trenton, Bensalem, Ewing, Princeton, Burlington,
Bristol, Hatboro, Pennington, Beverly, Rockledge and New Hope.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Turn around, don't drown when encountering flooded roads. Most flood
deaths occur in vehicles.
&&
LAT...LON 4026 7510 4034 7503 4036 7495 4034 7494
4034 7492 4035 7486 4038 7487 4040 7474
4038 7472 4039 7466 4038 7462 4032 7462
4029 7456 4013 7475 4013 7482 4008 7486
4005 7496 4005 7503 4013 7517
FLASH FLOOD...RADAR INDICATED
EXPECTED RAINFALL RATE...1-2 INCHES IN 1 HOUR
$$3 follow-up statements
153
WGUS71 KPHI 202319
FFSPHI
Flash Flood Statement
National Weather Service Mount Holly NJ
Issued by National Weather Service New York NY
719 PM EDT Thu Aug 20 2026
NJC021-PAC017-091-101-210230-
/O.CON.KPHI.FF.W.0124.000000T0000Z-260821T0230Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Mercer NJ-Bucks PA-Montgomery PA-Philadelphia PA-
719 PM EDT Thu Aug 20 2026
...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 1030 PM EDT THIS
EVENING FOR MERCER, SOUTHEASTERN BUCKS, EAST CENTRAL MONTGOMERY AND
NORTHEASTERN PHILADELPHIA COUNTIES...
At 719 PM EDT, local law enforcement reported thunderstorms producing
heavy rain with street flooding and road closures in Willow Grove.
Between 1 and 3 inches of rain have fallen. The expected rainfall
rate is 0.5 to 1 inch in 1 hour. Additional rainfall amounts up to 1
inch are possible in the warned area. Flash flooding is already
occurring.
HAZARD...Flash flooding caused by thunderstorms.
SOURCE...Law enforcement reported.
IMPACT...Flash flooding of small creeks and streams, urban areas,
highways, streets and underpasses as well as other poor
drainage and low-lying areas.
Some locations that will experience flash flooding include...
Philadelphia, Trenton, Bensalem, Ewing, Princeton, Burlington,
Bristol, Hatboro, Pennington, Beverly, Rockledge and New Hope.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Turn around, don't drown when encountering flooded roads. Most flood
deaths occur in vehicles.
&&
LAT...LON 4026 7510 4034 7503 4036 7495 4034 7494
4034 7492 4035 7486 4038 7487 4040 7474
4038 7472 4039 7466 4038 7462 4032 7462
4029 7456 4013 7475 4013 7482 4008 7486
4005 7496 4005 7503 4013 7517
FLASH FLOOD...OBSERVED
EXPECTED RAINFALL RATE...0.5-1 INCH IN 1 HOUR
$$959
WGUS71 KPHI 210046
FFSPHI
Flash Flood Statement
National Weather Service Mount Holly NJ
Issued by National Weather Service New York NY
846 PM EDT Thu Aug 20 2026
NJC021-PAC017-091-101-210230-
/O.CON.KPHI.FF.W.0124.000000T0000Z-260821T0230Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Mercer NJ-Bucks PA-Montgomery PA-Philadelphia PA-
846 PM EDT Thu Aug 20 2026
...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 1030 PM EDT THIS
EVENING FOR MERCER, SOUTHEASTERN BUCKS, EAST CENTRAL MONTGOMERY AND
NORTHEASTERN PHILADELPHIA COUNTIES...
At 846 PM EDT, local law enforcement reported flash flooding with
street flooding and road closures in Willow Grove. Between 1.5 and
3.5 inches of rain have fallen. Flooding impacts will continue, but
no additional rainfall is expected. Flash flooding is already
occurring.
HAZARD...Flash flooding caused by heavy rain.
SOURCE...Law enforcement reported.
IMPACT...Flash flooding of small creeks and streams, urban areas,
highways, streets and underpasses as well as other poor
drainage and low-lying areas.
Some locations that will experience flash flooding include...
Philadelphia, Trenton, Bensalem, Ewing, Princeton, Burlington,
Bristol, Hatboro, Pennington, Beverly, Rockledge and New Hope.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Turn around, don't drown when encountering flooded roads. Most flood
deaths occur in vehicles.
&&
LAT...LON 4026 7510 4034 7503 4036 7495 4034 7494
4034 7492 4035 7486 4038 7487 4040 7474
4038 7472 4039 7466 4038 7462 4032 7462
4029 7456 4013 7475 4013 7482 4008 7486
4005 7496 4005 7503 4013 7517
FLASH FLOOD...OBSERVED
$$
Hoeflich895
WGUS71 KPHI 210224
FFSPHI
Flash Flood Statement
National Weather Service Mount Holly NJ
Issued by National Weather Service New York NY
1024 PM EDT Thu Aug 20 2026
NJC021-PAC017-091-101-210234-
/O.EXP.KPHI.FF.W.0124.000000T0000Z-260821T0230Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Mercer NJ-Bucks PA-Montgomery PA-Philadelphia PA-
1024 PM EDT Thu Aug 20 2026
...FLASH FLOOD WARNING WILL EXPIRE AT 1030 PM EDT THIS EVENING FOR
MERCER, SOUTHEASTERN BUCKS, EAST CENTRAL MONTGOMERY AND NORTHEASTERN
PHILADELPHIA COUNTIES...
The heavy rain has ended. Flood waters have receded. Flooding is no
longer expected to pose a threat. Please continue to heed remaining
road closures.
&&
LAT...LON 4026 7510 4034 7503 4036 7495 4034 7494
4034 7492 4035 7486 4038 7487 4040 7474
4038 7472 4039 7466 4038 7462 4032 7462
4029 7456 4013 7475 4013 7482 4008 7486
4005 7496 4005 7503 4013 7517
$$
HoeflichThe office that day
Everything else NWS Philadelphia/Mount Holly issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 20, 2:04 PM EDT | Special Marine Warning | PHI | 86 min | |
| Aug 20, 3:26 PM EDT | Special Marine Warning | PHI | 94 min | |
| Aug 20, 4:38 PM EDT | Tornado Warning | PHI | Atlantic | 37 min |
| Aug 20, 4:41 PM EDT | Flash Flood Warning | PHI | Atlantic, Cape May, Cumberland | 4 hr |
| Aug 20, 5:13 PM EDT | Special Marine Warning | PHI | 92 min | |
| Aug 20, 5:14 PM EDT | Special Marine Warning | PHI | 91 min | |
| Aug 20, 5:24 PM EDT | Flash Flood Warning | PHI | Atlantic | 4 hr |
| Aug 20, 5:27 PM EDT | Severe Thunderstorm Warning | PHI | Gloucester, Salem | 48 min |
| Aug 20, 5:36 PM EDT | Special Marine Warning | PHI | 84 min | |
| Aug 20, 5:39 PM EDT | Flash Flood Warning | PHI | Camden, Gloucester, Salem | 4 hr |
| Aug 20, 6:09 PM EDT | Severe Thunderstorm Warning | PHI | Cumberland, Gloucester, Salem | 51 min |
| Aug 20, 6:13 PM EDT | Severe Thunderstorm Warning | PHI | Burlington, Camden, Gloucester, Mercer, Salem | 47 min |
| Aug 20, 6:15 PM EDT | Special Marine Warning | PHI | 60 min | |
| Aug 20, 6:30 PM EDT | Special Marine Warning | PHI | 90 min | |
| Aug 20, 6:38 PM EDT | Severe Thunderstorm Warning | PHI | Atlantic, Cape May, Cumberland | 37 min |
| Aug 20, 6:44 PM EDT | Special Marine Warning | PHI | 61 min | |
| Aug 20, 7:01 PM EDT | Tornado Warning | PHI | Atlantic, Cape May, Cumberland | 29 min |
| Aug 20, 7:08 PM EDT | Tornado Warning | PHI | Cape May | 22 min |
| Aug 20, 7:10 PM EDT | Severe Thunderstorm Warning | PHI | Atlantic, Cape May, Cumberland | 50 min |
| Aug 20, 7:37 PM EDT | Special Marine Warning | PHI | 2 hr | |
| Aug 20, 7:43 PM EDT | Special Marine Warning | PHI | 2 hr | |
| Aug 20, 4:50 PM EDT | Severe Thunderstorm Warning | PHI | Berks, Chester | 40 min |
| Aug 20, 4:59 PM EDT | Severe Thunderstorm Warning | PHI | Chester | 46 min |
| Aug 20, 5:22 PM EDT | Tornado Warning | PHI | Chester, Delaware | 38 min |
Nearby
Flash Flood Warnings in Pennsylvania, 2026Flash Flood Warnings in New Jersey, 2026Every flash flood warning in 2026
Sources
The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.